Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft and housed in a compressor housing. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the turbine housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
In a turbocharger, it is often desirable to control the flow of exhaust gas to the turbine to improve the efficiency or operational range of the turbocharger. Variable geometry turbochargers have been configured to address this need. A type of such variable geometry turbocharger is one having a variable exhaust nozzle, referred to as a variable nozzle turbocharger. Different configurations of variable nozzles have been employed in variable nozzle turbochargers to control the exhaust gas flow. One approach taken to achieve exhaust gas flow control in such variable nozzle turbochargers involves the use of multiple pivoting vanes that are positioned annularly around the turbine inlet. The pivoting vanes are commonly controlled to alter the throat area of the passages between the vanes, thereby functioning to control the exhaust gas flow into the turbine.
In order to ensure the proper and reliable operation of such variable nozzle turbochargers, it is important that the individual vanes be configured and assembled within the turbine housing to move or pivot freely in response to a desired exhaust gas flow control actuation. FIG. 1 illustrates a prior art vane 10 used in such turbocharger application, comprising an outer airfoil surface 12, and inner airfoil surface 14, and opposed axial surfaces 16 and 18. This type of vane is one having a “solid” construction because the vane axial surfaces 16 and 18 are defined by a continuous planar or flat structure.
While such conventional solid vanes 10 are useful in variable geometry turbochargers, the solid design of the vanes is known to make vane mobility within the turbocharger more difficult, and is known to impose related friction effects on the vanes and related vane movement mechanisms within the turbocharger that can reduce operational service life of the turbocharger. Additionally, the cost associated with using solid vanes is relatively expensive.
FIGS. 2A and 2B each illustrate another prior art vane 20 that is constructed having a non-solid construction. Specifically, such prior art vane 20 is configured having axial surfaces 22 and 24 that, unlike the solid vane discussed above, have axial surfaces that are substantially cored or hollowed-out.
As illustrated in FIG. 2A, vane axial surface 22 is defined by two cored-out sections 26 and 28 that together occupy a major portion of the axial surface area. The vane axial surface 22 includes a solid section 30, that is disposed between the two cored-out sections 26 and 38, and that represents a minor portion of the axial surface area. As illustrated in FIG. 2B, vane axial surface 24 is defined by two cored-out sections 32 and 34 that together occupy a major portion of the of the axial surface area. The vane axial surface 24 includes an opening 36 disposed between the two cored-out sections, and is positioned opposite from the solid section 30 of the opposed vane axial surface 22.
This prior art cored-out vane is useful in providing a vane structure having reduced weight, thereby reducing the effort and frictional wear associated with moving vanes of this construction within a turbocharger, and having a reduced expense. However, the cored-out structure of such vanes may operate to permit undesired air flow effects to occur within the turbocharger. For example, the cored-out vane axial surfaces may operate to provide a leak path for air directed onto the vane's airfoil surfaces. For example, air being directed to the vane leading edge and airfoil surfaces, rather then being directed along the airfoil surfaces, can leak between the vane axial surfaces and adjacent turbocharger surfaces due to the reduced resistance to airflow that is provided by the core-out configuration. Such vane leakage within the turbocharger is not desired as it adversely impacts turbocharger operating efficiency.
It is, therefore, desired that a vane be constructed for use within a variable geometry turbocharger that has a reduced weight, when compared to a conventional solid construction vane, and that minimizes or eliminates unwanted airflow effects within the turbocharger associated with air leakage across the vane, thereby providing improved vane operational reliability and turbocharger efficiency.